Toolmaking at G.RAU covers an unusually wide range of activities. In addition to typical products such as multi-stage operation dies for stamped/bent components, deep-drawing and extrusion molds as well as jigs and fixtures, the company creates prototypes for medical instruments for a range of customers that includes Pforzheim-based affiliates EUROFLEX and ADMEDES SCHUESSLER, which operate in the field of medical engineering. The requirements regarding the five-axis milling centre, which was acquired as part of a modernisation programme at the department in 2010, are equally diverse. It must be capable of machining parts up to one metre long on the one hand, while meeting extreme requirements in terms of accuracy on the other. In the end, the company opted for a DMG DMU 80 monoBLOCK that provided the machining space required. To facilitate the use of very small tools as well, it was equipped with a higher-speed spindle, which can reach up to 24,000 rpm. Included in the machine's scope of delivery were a laser tool measuring system from Blum-Novotest GmbH as well as a touch probe from another manufacturer. The LaserControl Micro Compact NT tool measuring system is located on the rear edge of the machine table and is used for calibrating new tools and for wear measurement and compensation. The focussed laser beam makes it possible to measure the length of even extremely thin tools just as precisely as the actual diameter.
With the help of these measurements, worn and chipped spots on the cutting edges can be measured very precisely. All tools are measured, from the spherical cutter with a diameter of 0.5 millimetres to the cutter head measuring 50 mm across. For Marcel Heinz, who heads the toolmaking production team, the advantages of tool setting in the machine are obvious: "It completely eliminates the need for tool pre-setters. Instead of painstakingly measuring new tools on an external measuring station and entering the values manually into the control system, the geometry is recorded directly in the machine and stored in the tool database in the control system. This eliminates errors on the one hand while reassuring us that the values recorded are actually correct on the other. Ultimately, the tools are measured using the laser system under the same conditions in which they are subsequently used for machining, that is, clamped in the spindle and operating at nominal spindle speeds."
The company also uses the laser system for tool breakage detection, which saves money. A broken tool can cause enormous damage, for example, if the machine or the NC program running on it assumes that a roughing procedure has actually been performed. If the roughing tool breaks during the machining process, much more material will still be present than the program requires. Consequently, the next tool will collide with the workpiece, potentially destroying the tool and, in the worst case scenario, causing damage to the spindle and the machine. Due to the stylus with a diameter of 4 mm, the touch probe supplied with the machine proved to be useless particularly on very small workpieces. A stylus tip with a diameter of no more than 0.5 mm is required for measuring inside contours. According to the manufacturer, this was not possible with the existing touch probe, which is why G.RAU finally turned to Blum-Novotest. Since its laser tool measuring system had already performed impressively, the new touch probe was also ordered from BLUM. As it turned out, the measurement technology specialist from Upper Swabia delivered exactly what was required: The TC52 LF is a compact touch probe, whose low-force version operates with a very low measuring force and can therefore be equipped with a 0.5 millimetre stylus tip.
On a one-day visit to the head office of Blum-Novotest GmbH in Grünkraut near to Ravensburg, measurements were conducted on a comparable milling machine. The results immediately impressed and the touch probe was ordered there and then. Thanks to the multi-directional measuring mechanism, the BLUM probe system does not return different measurement results when probing in different directions compared with many other probes, which also helps to meet the high level of accuracy required here. Constant measuring forces in any probing direction are the prerequisite for precise measurement results. The probe system is automatically substituted from the tool magazine into the spindle just like a tool. The power supply is provided by a long-life battery and the data is transmitted by infra-red communication to the receiver fitted to the spindle head of the machine.
"A key factor that influenced the decision in favour of the TC52 LF was that BLUM could also supply measuring software with the touch probe", recalls Heinz. "Until then, we could only approach the workpiece using the touch probe and read the measurement from the screen of the machine. The FormControl software allows us to do a great deal more." Machine operator Ralph Bauer loads the CAD model of the workpiece, which is provided in Pro/Engineer format by the design department, into FormControl, which runs on the same computer at G.RAU as the hyperMill CAM software. On the displayed geometry, Bauer can now define the desired measuring points, the permitted tolerances, and the measuring sequence. From this, FormControl generates an NC programme that is transferred to the machine. After the measurement is complete, the values determined are fed back into the software. These can be issued as a measuring report or graphically displayed on the monitor, e.g., using coloured needles. To do this, FormControl compares the measured values with the CAD geometry and the tolerances entered, and then marks values that are outside the tolerance in red, and values within the specifications in green. Likewise, undersized and oversized areas can be highlighted in colour. "This gives us a quick overview", says Bauer.
FormControl is extremely user-friendly: A half-day instruction course from a BLUM technician is all that's required to master the system. Bauer adds: "After this introduction, we didn't need any further support; the system runs perfectly and doesn't throw up any issues." The cutting knives used to trim the upper edge of a "cup-shaped" workpiece are a good example of what the BLUM probe system is capable of in practice. Heinz outlines the challenges: "The tolerances on these components are extremely fine, just as they are on the cutting knives – whose blade clearance is just 5 micrometres wide. The blades are arranged in a star formation and cut outwards in a radial movement. We manufacture the cutting knives from a single block of powder injected steel. One block provides two sets of twelve knives. First of all, the geometry is milled and then the cuts eroded. It all has to fit perfectly."
Bauer mills the blocks in several steps. To begin with, he stays one or two hundredths of a millimetre outside the final geometry and then reduces the measurements accordingly by a process of measurement and further milling. In doing so, he benefits from the BLUM touch probe's ability to perform contour measurements. He creates a 3D model of the actual contour of the important geometrical areas of the block and knows exactly where and how much he needs to mill in the next machining step. The colour coding of oversize dimensions in the measuring report helps him quickly identify the areas to be machined. Two very precise bores, which Bauer creates during the milling operation, connect the machining processes and are used to position the workpiece in the EDM machine. "These cutting tools are extremely expensive," explains Heinz. "The material is very expensive, and we then invest two days of milling time plus 50 to 60 hours of erosion in it." Without the touch probe, however, these tools were even more expensive, as Heinz explains further: "We simply could not manufacture these components without contour measurement and the small stylus diameter of the BLUM probe system. For this reason, these components were manufactured by a service provider, which cost twice as much as in-house production." Bauer mentions another key aspect: "If the production department needs a replacement part, our in-house toolmaking department can respond much more quickly than if we were to have the part made externally."
The precision enabled by measuring in the chuck on the machine tool is an important factor, as Bauer explains: "If we manufacture and measure the tool ourselves, we can be sure that all dimensions are correct down to a few micrometres. There is nothing worse than having a tool on the production line break, only to discover that the available replacement does not meet the tolerances required. In the worst case, this can result in the machine standing idle for an extended period – and then the costs really start to mount." The LaserControl Micro Compact NT laser measuring system also saves time, as Bauer sums up: "Instead of carrying out external measurements on presetting equipment, which then have to be manually transferred, the results are transmitted directly to the machine control system in less than one minute. This is very quick and it allows us to measure the tools during every tool change without losing too much time. This in turn also helps us achieve the high precision of our workpieces." "If you consider that we take measurements on a machining system in a hall that is not air-conditioned, the accuracy that we need to achieve is pretty astonishing," agrees Marcel Heinz. "The BLUM products really impressed us! With the help of the FormControl measuring software and the touch probe, we can achieve our high accuracies without difficulty. An additional machine with a pre-installed laser measuring system by Blum-Novotest is already in the pipeline. We have completed all preparations to enable the use of the touch probe and FormControl on another machine."
Founded in 1877, G.RAU GmbH & Co. KG is a world-leading specialist for innovative solutions covering all aspects of metal, and a preferred supplier to renowned companies in various fields of electrical and automotive engineering, measurement and control industries as well as medical engineering. From semi-finished products to complex functional assemblies, G.RAU offers everything from a single source. In addition to G.RAU GmbH & Co. KG, the group includes a range of other companies such as Pforzheim-based EUROFLEX GmbH and ADMEDES Schuessler GmbH – both of which are market leaders in sub-segments of the medical engineering industry.